J. Phys. Chem. C 2008, 112, 1244-1249
Photoinduced Intramolecular Electron Transfer of Carbazole Trimer-Fullerene Studied by Laser Flash Photolysis Techniques Takashi Konno,† Mohamed E. El-Khouly,‡,§ Yosuke Nakamura,*,† Keisuke Kinoshita,† Yasuyuki Araki,‡ Osamu Ito,‡ Toshitada Yoshihara,† Seiji Tobita,† and Jun Nishimura† Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma UniVersity, Tenjin-cho, Kiryu, Gunma 376-8515, Japan, Institute of Multidisciplinary Research for AdVanced Materials, Tohoku UniVersity, Katahira, Aoba-ku, Sendai 980-8577, Japan, and Department of Chemistry, Faculty of Education, Tanta UniVersity, Egypt ReceiVed: August 9, 2007; In Final Form: October 24, 2007
Photoinduced intramolecular events of newly synthesized bis(carbazole trimer)-C60 adducts have been studied by laser flash photolysis techniques in polar and nonpolar solvents. For bis(tert-butyl-substituted carbazole trimer)-C60 adduct, charge separation takes place via the excited singlet state of the C60 moiety in polar solvents as revealed by the combination of the C60-fluorescence quenching and transient absorptions of the radical ion pair. On the other hand, for bis(nonsubstituted carbazole trimer)-C60 adduct, although charge separation takes place, the charge recombination is fast because of the lower electron-donor ability.
Introduction Photoinduced intramolecular electron-transfer processes in donor-acceptor systems are of considerable interest and importance from the aspects of light-energy conversion in relation to the photosynthetic reaction.1 Fullerenes, which possess a unique three-dimensional π-electron system, have been well known as excellent electron acceptors.2 Since the functionalization of fullerenes have been developed, a variety of C60 adducts covalently linked with donor moieties have been synthesized, and their photophysical properties, especially the photoinduced electron transfer, have been clarified.3 The efficient charge separation (CS) and slow charge recombination (CR) were accomplished by using C60 as electron acceptor due to its small reorganization energy.4 The efficiencies and rates of the electron-transfer processes in the donor-C60 dyads depend on the energy of CS state for the donor-C60 pair, the distances and orientations between the donor and C60 moieties, and the type of linkages connecting them.5 As electron donors, olefins, aromatic amines, porphyrins, phthalocyanines, ruthenium complexes, ferrocenes, tetrathiafulvalenes, and oligothiophenes have been employed for the preparation of fullerene-based dyads and triads.6 Among the amine-C60 dyads, various triphenylamine-C60 dyads and N,N-dimethylaniline-C60 dyads have been synthesized with changing the linkages, and their photophysical properties have been extensively investigated extensively.7 Carbazole, known as a component of photoconductive poly(N-vinylcarbazole) (PVCz), is also one of the typical aromatic amines and good electron donors.8 While the intermolecular photoinduced electron transfer between carbazole derivatives and fullerenes has been well investigated,9 there have been only a few examples of the intramolecular photoinduced electron transfer of carbazole-linked C60 dyads. The N-ethylcarbazoleC60 (EtCz-C60) prepared by Prato reaction generated the CS * Corresponding author. E-mail: [email protected]
† Gunma University. ‡ Tohoku University. § Tanta University.
state with a lifetime of 300 ns in N,N-dimethylformamide (DMF).10 Recently, we have successfully prepared C60 adduct (MCz-C60) bearing a monocarbazole moiety by using Bingel reaction (MCz denotes monocarbazole).11 However, the photoinduced electron transfer via the excited states of C60 was not evidently detected in MCz-C60. One of the reasons for the failure to observe the photoinduced electron transfer is the lack of the electron-donating ability of the carbazole moiety in MCz-C60. Therefore, we were prompted to utilize trimeric carbazole moieties with more electron-donating ability than the single carbazole systems in MCz-C60.12 The larger π-conjugated system in carbazole trimer enables the delocalization of positive charge in the CS state, leading to the slow CR process. Recently, it has been reported that multiple donor attachments to C60 improve the photoinduced electron-transfer characters.13 Thus, in the present study, we have synthesized two novel C60 adducts, TCz-C60 and tTCz-C60, bearing dual carbazole trimer moieties attached to the cyclopropane ring symmetrically (TCz and tTCz denote carbazole trimer and t-butyl-substituted carbazole trimer, respectively). The t-butyl groups in tTCz-C60 are expected to further enhance the electron-donating ability. Herein, we disclose the photophysical properties of TCz-C60 and tTCz-C60, mainly focusing on their CS and CR processes. Results and Discussion Synthesis of Materials. Scheme 1 depicts the synthetic sequence of bis(carbazole trimer)-C60 adducts, TCz-C60 (5a) and tTCz-C60 (5b). The synthetic procedure was described in detail in Supporting Information. The palladium-catalyzed coupling reactions of carbazole trimers, TCz (1a)14a and tTCz (1b),14b with p-bromobenzaldehyde gave aldehydes 2a and 2b.15 The NaBH4-reduction, followed by the reaction with malonyl dichloride, afforded malonate esters TCzME (4a) and tTCzME (4b). The Bingel reaction of C60 with TCzME and tTCzME provided TCz-C60 and tTCz-C60 in moderate yields. Both TCz-C6013 and tTCz-C60 were characterized by 1H and 13C NMR, atmospheric pressure chemical ionization (APCI)-mass, and UV/vis spectroscopies as summarized in Experimental Section.
10.1021/jp076387a CCC: $40.75 © 2008 American Chemical Society Published on Web 01/09/2008
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Figure 1. Steady-state absorption spectra of tTCz-C60, tTCz, and C60C(COOEt)2 (0.1 mM) in CH2Cl2.
Photoinduced Intramolecular Events. Figure 1 shows the steady-state absorption spectra of tTCz-C60, tTCz, and C60C(COOEt)2 in CH2Cl2. The spectral features of tTCz-C60 in the visible range showing absorption bands at 695 and 430 nm are characteristic of the fullerene entity as demonstrated in C60C(COOEt)2 (bis(ethoxycarbonyl)methano-fullerene). The absorption bands in the UV range (<400 nm) correspond to both fullerene and tTCz entities. Appreciable increase of the absorbance of tTCz-C60 was observed in the 450-500 nm region compared with the component, suggesting slight interaction between tTCz and C60 moieties in their ground states. Similar spectra were obtained in other solvents. TCz-C60 showed almost the same spectra as tTCz-C60. The photoinduced intramolecular events of TCz-C60 and tTCz-C60 were investigated, first, by the steady-state fluorescence spectra. Figure 2 depicts the spectra of tTCz-C60 in toluene (TN) and DMF. The fluorescence spectrum of tTCz-
C60 observed with visible light excitation in TN is similar to those of typical C60 monoadducts such as C60C(COOEt)2; the fluorescence of the C60 moiety is hardly quenched by the appendent tTCz moiety. In polar DMF, however, efficient C60fluorescence quenching was observed. Such observations suggest efficient quenching of the singlet state of the C60 moiety (1C60*) by the appended carbazole trimer entities in only polar solvents. Similar results were obtained for TCz-C60; the fluorescence of C60 moiety is almost quenched in DMF. With UV-light excitation, fluorescence spectra were almost the same as those with visible-light excitation, because UV light predominantly excites the C60 moiety with a small fraction of the TCz or tTCz moiety; even if the TCz or tTCz moiety is excited, the energy transfer to the C60 moiety efficiently takes place. By using the streakscope as a detector, the fluorescence spectra were observed by applying the 400 nm laser light in the time range 0-2 ns as shown in Supporting Information (Figure S1). Although significant quenching of the 1C60* moiety was observed in DMF, a fluorescence peak was found near 700 nm. Fluorescence lifetime measurements of TCz-C60 and tTCzC60 track the above considerations in a more quantitative way, giving kinetic data of the charge-separation processes. As shown
SCHEME 1: Synthetic Routes of Bis(carbazole Trimer)-C60 Adducts, tTCz-C60 and TCz-C60
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Konno et al.
Figure 2. Steady-state fluorescence spectra of tTCz-C60 (0.1 mM) in TN and DMF; λex ) 430 nm.
cyclic voltammogram of the tTCz-C60 in benzonitrile (PhCN), which gave sharper peaks than DMF due to higher solubility, recorded the first reduction potential (Ered) of the C60 moiety at -950 mV versus Fc/Fc+, while the first oxidation potential (Eox) of the tTCz was located at 580 mV versus Fc/Fc+. The potential difference between the first Eox and Ered was found to be 1.53 eV. The Eox of the donor moieties in TCz-C60 was located at 780 mV versus Fc/Fc+, which is 200 mV higher than that of tTCz-C60, reflecting the lower donor ability of the TCz moiety compared with tTCz moiety. On the basis of the first Eox of the carbazole trimer moiety, the first Ered of the C60 moiety and a solvent correction term (∆GS), the driving forces for the CR process (-∆GCR) and the CS process (-∆GCS) via 1C60* were calculated from the Rehm-Weller equation as follows:17
-∆GCR ) e(Eox - Ered) + ∆GS
-∆GCS ) ∆E00 - (-∆GCR)
∆E00 is the energy of the 0-0 transition (1.75 eV for 1C60*), and ∆GS was calculated by the following equation:17 Figure 3. Time profiles of 1C60* emission at 700 nm of tTCz-C60 in TN and DMF; λex ) 400 nm.
TABLE 1: Free-Energy Changes for CS Process (-∆GCS), Fluorescence Lifetimes (τf), and Rates (kCS) and Quantum Yields (ΦCS) of CS Process of tTCz-C60 and TCz-C60 via 1C60* in Toluene and DMF compound solvent -∆GCS/eV τf /ps (fraction%) tTCz-C60
110 (58%) 720 (42%) 1400 (100%) 190 (75%) 950 (25%) 1400 (100%)
7.80 × 109 0.91 6.88 × 108 0.50 4.56 × 109 0.86 3.52 × 108 0.33
in Figure 3, fluorescence time-profile of tTCz-C60 in toluene revealed a monoexponential decay of the 1C60* moiety with a lifetime of 1400 ps (τf), which is similar to the lifetime of C60 reference (τf0). On the other hand, the fluorescence decay in DMF was clearly not monoexponential, which can be attributed to the presence of more conformations of the tTCz moiety with respect to the C60 unit. The time profiles of tTCz-C60 could be approximately fitted to biexponential decays, where the major short lifetimes were found to be 110 ps in DMF. For TCzC60, the major short lifetime in DMF was found to be 190 ps. These findings support an efficient deactivation of the 1C60* moiety by the attached carbazole trimer moieties in polar solvents. In general, energy transfer and electron transfer can be thought as an origin of fluorescence deactivation, but the charge separation is predominant in this case, because the energy level of the 1C60* moiety is lower than that of carbazole trimer unit. Thus, by using the short lifetimes of tTCz-C60 and TCzC60 and the lifetime of C60 reference, the rates (kCS) and quantum yields (ΦCS) for the CS processes were evaluated from the following equations:16
kCS ) (1/τf) - (1/τf0)
ΦCS ) kCS/(1/τf)
The kCS (ΦCS) values of tTCz-C60 were evaluated as 7.80 × 109 s-1 (0.91) in DMF. Less efficient CS process was observed for the TCz-C60 adduct as listed in Table 1. The CS process via the 1C60* was supported from the viewpoint of thermodynamics of electron-transfer processes. The
-∆GS ) -(e2/(4π0))[(1/(2R+) + 1/(2R-) 1/RCC)/S - (1/(2R+) + 1/(2R-))/R (5) where R+ and R- are radii of the radical cation (6.0 Å) and radical anion (4.2 Å), respectively, as evaluated from the molecular orbital (MO) calculations; RCC is the center-center distance between C60 and donor (ca. 12 Å), which were evaluated from the optimized structure in the next paragraph; R and S refer to solvent dielectric constants for electrochemistry and photophysical measurements, respectively. The -∆GCS values in DMF were evaluated as 0.30 and 0.10 eV for tTCzC60 and TCz-C60, respectively. These values suggest exothermic CS process via the 1C60* moiety to form the radical ion pairs in polar solvents whereas endothermic in toluene. Moreover, the CS process from the carbazole trimer unit to the 1C60* moiety to form the radical ion pair (TCz•+-C60•-) was supported by MO calculation studies. On the basis of the density functional method at the B3LYP/3-21G* level after optimizing the structure,18 the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of TCz-C60 were obtained as shown in Figure 4. In the optimized structure, two carbazole trimers cover the spherical C60 moiety as open wings of a bird, although two carbazole trimers are not completely symmetric. In each carbazole trimer, three carbazoles are not at equal position to C60; that is, one terminal carbazole unit of the carbazole trimer is closer to the C60 moiety, whereas another is far from the C60 moiety. Although the two terminal carbazole units in each carbazole trimer are not coplanar with respect to the central carbazole unit, the HOMO and HOMO-1, which are almost degenerated, spread over the right and left three carbazole units, respectively. Thus, in the one-electron oxidation state of TCz-C60 the radical cation delocalized over the three carbazoles. The RCC was evaluated as an averaged distance from the center of C60 to the center of three nitrogen atoms in carbazole trimer to be 11.8 Å. A similar optimized structure was obtained for tTCz-C60 with RCC ) 12.0 Å (Supporting Information, Figure S2). The majority of the electron distribution of the LUMO is located on the C60 moiety; therefore, the charge-separated state was presumed as a radical cation localized on the carbazole trimer unit and a radical anion localized on the C60 moiety
J. Phys. Chem. C, Vol. 112, No. 4, 2008 1247
Figure 4. Optimized structure calculated by MO method (C, gray; O, red; N, blue; and H, white) and the HOMO, HOMO-1, and LUMO of TCz-C60 obtained with DFT (B3LYP/3-21G*) method.
TABLE 2: Free-Energy Changes for CR (-∆GCR), Rates of CR (kCR), and Lifetimes of Radical Ion Pairs (τRIP) of tTCz-C60 and TCz-C60 in Toluene and DMF compounds tTCz-C60 TCz-C60
Figure 5. Nanosecond transient spectra obtained by 355 nm laser light of tTCz-C60 adduct (0.13 mM); (a) in Ar-saturated toluene and (b) in Ar-saturated DMF. Inset: time profiles.
(TCz•+-C60•-). Similar results were obtained for tTCz-C60, predicting tTCz•+-C60•- (Supporting Information, Figure S2). In the case of TCz-C60, the orbital energy of the LUMO was found to be -3.61 eV, while the orbital energies of the HOMO and HOMO-1 were found to be -5.30 and -5.32 eV, respectively. Thus, the average value of the calculated HOMOLUMO gap is 1.70 eV, which is quite similar to the electrochemically obtained HOMO-LUMO gap (1.73 eV). The nanosecond transient spectra of tTCz-C60 were obtained by 355 nm laser light, which excites mainly the C60 moiety with small fraction of tTCz moiety as evaluated from the steadystate absorption spectrum. In toluene (Figure 5a), the absorption spectra exhibited only the absorption peak at 700 nm, which is attributed to the triplet state of C60 (3C60*).19,20 In DMF (Figure 5b), a decisive evidence for the CS from the carbazole trimer to the C60 was observed from the transient spectra, which
solvent DMF toluene DMF toluene
-∆GCR/eV 1.45 1.97 1.65 2.17
3.3 5.0 ×107 -
τRIP/ns 300 20 -
exhibited absorption bands of the radical ion pairs in the nearIR region; that is, the peak at 1020 nm is characteristic of the C60•- moiety,21 and the broad absorptions with a maximum at 1080 nm are most likely to be assigned to the tTCz•+ moiety. This assignment was confirmed by the observed absorption spectra by mixing tTCz-C60 with FeCl3, which exhibited new peak around 1100 nm and weak broad band appeared in the 1200-1400 nm region as a result of one-electron oxidation of the tTCz moiety, giving tTCz•+ (Supporting Information, Figure S3). The time profiles of tTCz•+ and C60•- were curve-fitted by a single-exponential and gave similar decay rate constant from which the rate constant of the CR process (kCR) of tTCz•+C60•- in DMF was evaluated as 3.3 × 106 s-1. From the value of kCR, the lifetime of the radical ion pairs tTCz•+-C60•- (τRIP) was evaluated as 300 ns (Table 2). For TCz-C60, the transient spectra in DMF exhibited the absorption peaks of the 3C60*, C60•-, and TCz•+ moieties with 355 nm laser excitation as shown in Figure 6. The absorption intensity of the 3C60* moiety of TCz-C60 was remarkably higher than that of tTCz-C60, which reflects the lower electrondonor ability of TCz compared with that of tTCz. From the initial decay at 1080 nm, the kCR value in DMF was evaluated as 5.0 × 107 s-1, which gave the τRIP of TCz•+-C60•- to be 20 ns. The solvent effects can be interpreted by the relative energy level of the RIP with respect to 3C60*. As shown in the energy diagram in Figure 7, in highly polar solvents such as DMF the energy level of tTCz•+-C60•- (1.45 eV) is lower than that of 3C * (1.50 eV); therefore, the CR process takes place going to 60 the ground state, which belongs to the inverted region of the Marcus parabola,22 because of the small reorganization energy of the fullerene derivatives, usually ca. 0.6 eV.4 Appreciable different behavior between tTCz•+-C60•- and TCz•+-C60•- can be explained by the same concept (Figure 7) because of 200 mV difference in the first Eox. In the case of
1248 J. Phys. Chem. C, Vol. 112, No. 4, 2008
Figure 6. Nanosecond transient spectra obtained by 355 nm laser light of TCz-C60 (0.13 mM) in Ar-saturated DMF. Inset: time profile.
Figure 7. Energy diagram for photoinduced processes of tTCz-C60 and TCz-C60.
TCz•+-C60•-, because the energy level of TCz•+-C60•- (1.65 eV in DMF) is higher than that of the 3C60* moiety, the CR process going to the 3C60* moiety quickly takes place in the normal region of the Marcus parabola.22 Conclusions Photoinduced intramolecular charge-separation process of newly synthesized bis(carbazole trimer)-C60 adducts has been studied by laser flash photolysis techniques in polar and nonpolar solvents. As summarized in energy diagrams illustrated in Figure 7, for bis(tert-butyl-substituted carbazole trimer)-C60, charge separation takes place via the excited singlet state of the C60moiety in highly polar solvents such as DMF as revealed by the combination of the C60-fluorescence quenching and transient absorptions of the radical ion pair. On the other hand, for bis(nonsubstituted carbazole trimer)-C60, although charge separation takes place in DMF, the charge recombination is fast because of the lower electron-donor ability of the nonsubstituted carbazole trimer. In addition to the substituents on the carbazole trimer, the solvent polarity also drastically controlled the chargeseparation process and charge-recombination process. Experimental Section Materials. Synthesis of TCz-C60.14 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) (93 mg, 0.61 mmol) was added to a mixture
Konno et al. of C60 (147 mg, 0.20 mmol), TCzME (260 mg, 0.20 mmol), and CBr4 (135 mg, 0.41 mmol) in toluene (200 mL) at room temperature, and the mixture was stirred for 7 h under a nitrogen atmosphere. The crude material was filtered through a short column (silica gel), eluting first with hexane to remove unreacted C60 and then with toluene/hexane (1:1), to give monoadduct 5a. This fraction was further purified by GPC (solvent; CHCl3) to give 5a (65 mg, 15.9%). 1H NMR (CDCl3, 500 MHz): δ 8.24 (s, 4H), 8.13 (d, J ) 8.0 Hz, 8H), 7.85 (d, J ) 8.5 Hz, 4H), 7.77 (d, J ) 8.0 Hz, 4H), 7.61 (d, J ) 9.0 Hz, 4H), 7.54 (dd, J ) 8.8 Hz, 4H), 7.37-7.34 (m, 16H), 7.28-7.24 (m, 8H), 5.71 (s, 4H). 13C NMR (CDCl3, 125 MHz): δ 163.5, 145.2, 145.1, 144.9, 144.8, 144.7, 144.6, 144.5, 144.4, 143.7, 143.0, 142.9, 142.8, 142.0, 141.6, 141.5, 140.9, 140.2, 138.9, 137.8, 134.4, 131.1, 130.6, 128.3, 127.2, 126.2, 125.9, 124.1, 123.1, 120.3, 119.7, 111.2, 109.6, 71.2, 68.3, 51.5. APCI-MS: m/z 1992 (M-). Synthesis of tTCz-C60. DBU (113 mg, 0.74 mmol) was added to a mixture of C60 (178 mg, 0.25 mmol), tTCzME (426 mg, 0.25 mmol), and CBr4 (164 mg, 0.49 mmol) in hexane (300 mL) at room temperature, and the mixture was stirred for 8 h under a nitrogen atmosphere. The crude material was filtered through a short column (silica gel), eluting first with toluene to remove unreacted C60 and then with toluene/hexane (1:1), to give monoadduct 5b. This fraction was further purified by GPC (solvent; CHCl3) to give 5b (131 mg, 21.8%). 1H NMR (CDCl3, 500 MHz): δ 8.23 (s, 4H), 8.15 (s, 8H), 7.87 (d, J ) 8.5 Hz, 4H), 7.79 (d, J ) 8.0 Hz, 4H), 7.61 (d, J ) 9.0 Hz, 4H), 7.56 (dd, J ) 9.0 Hz, 4H), 7.43 (dd, J ) 8.5 Hz, 8H), 7.31 (d, J ) 8.5 Hz, 8H), 5.74 (s, 4H), 1.45 (s, 72H). 13C NMR (CDCl3, 125 MHz): δ 163.5, 145.2, 145.0, 144.9, 144.7, 144.6, 144.5, 144.3, 143.7, 143.0, 142.9, 142.8, 142.6, 142.0, 141.6, 140.9, 140.0, 139.9, 138.9, 137.9, 134.3, 131.0, 127.2, 125.9, 124.1, 123.6, 123.1, 119.3, 116.2, 111.0, 109.1, 71.2, 68.3, 51.5, 34.7, 32.0. Instruments. Electrochemical redox potential values were measured by the cyclic voltammetry (CV) technique by applying a Hokuto HAB-151 potentiostat/galvanostat with a function generator. A platinum disk electrode was used as the working electrode with a platinum wire and an Ag/Ag+ electrode serving as the counter and reference electrodes, respectively. All measurements were carried out in PhCN solvent containing (nBu)4N+PF6- (0.1 M) as a supporting electrolyte in a scan rate of 0.2 V s-1. Steady-state absorption spectra were measured with JASCO UV/vis/near-IR spectrophotometer and a HITACHI U-3210 spectrophotometer. Steady-state fluorescence spectra were collected on a Shimadzu RF-5300 PC spectrofluorophotometer equipped with a photomultiplier tube having high sensitivity in the 700-800 nm region and a HITACHI F-4500 spectrophotometer. Fluorescence lifetimes were measured by a singlephoton counting method using a second harmonic generation (SHG, 400 nm) of a Ti:sapphire laser (Spectra-Physica, Tsunami 3950-L2S, 1.5 ps fwhm) and a streakscope (Hamamatsu Photonics) equipped with a polychromator as an excitation source and a detector, respectively.23 Nanosecond transient absorption measurements in the near-IR region were carried out by laser flash photolysis using an excitation light source of Nd: YAG laser (Spectra-Physics and Quanta-Ray GCR-130, 6 ns fwhm). Monitoring lights from a pulsed Xe-lamp were detected via Ge-avalanche photodiode module.24 Prior to the measurement, the sample solution in a quartz cell (1.0 × 1.0 cm) was deaerated by bubbling argon gas for a period of 20 min.
Carbazole Trimer-Fullerene Supporting Information Available: Synthetic details, fluorescence spectra measured by streak-scope, MO calculation data. This material is available free of charge via the Internet at http:// pubs.acs.org. References and Notes (1) (a) Connolly, J. S.; Bolton J. R. In Photoinduced Electron Transfer; Fox, M. A., Chanon M., Eds.; Elsevier: Amsterdam, 1988. (b) Mataga, N.; Miyasaka, H. In Electron Transfer; Jortner, J., Bixon, M., Eds.; John Wiley & Sons: New York, 1999; Part 2, pp 431-496. (c) Balzani V., Ed. Electron Transfer in Chemistry; Wiley-VCH: Weinheim, 2001; Vols. I-V. (2) (a) Guldi, D. M.; Kamat, P. V. In Fullerenes, Chemistry, Physics and Technology; Kadish, K. M.; Ruoff, R. S., Eds.; Wiley-Interscience: New York, 2000; pp. 225. (b) Fujitsuka, M.; Ito, O. Photochemistry of Fullerenes. In Handbook of Photochemistry and Photobiology; H. S. Nalwa, Ed.; American Scientific Publisher: New York, 2003; Vol. 2, Chapter 2, pp 111-145. (3) (a) Imahori, H.; Sakata, Y. AdV. Mater. 1997, 9, 537. (b) Guldi, D. M.; Prato, M. Acc. Chem. Res. 2000, 33, 695. (c) Otsubo, T.; Aso, Y.; Takimiya, K. J. Mater. Chem. 2002, 12, 2565. (d) Segura, J. L.; Martin, N.; Guldi, D. M. Chem. Soc. ReV. 2005, 34, 31. (e) Martı´n, N. Chem. Commun. 2006, 2093-2104. (4) (a) Imahori, H.; Hagiwara, K.; Akiyama, T.; Akoi, M.; Taniguchi, S.; Okada, T.; Shirakawa, M.; Sakata, Y. Chem. Phys. Lett. 1996, 263, 545. (b) Tkachenko, N. V.; Rantala, L.; Tauber, A. Y.; Helaja, J.; Hynninen, P. H.; Lemmetyinen, H. J. Am. Chem. Soc. 1999, 121, 9378. (c) Fukuzumi, S.; Guldi, D. M. In Electron Transfer in Chemistry; Balzani, V., Ed.; WileyVCH: Weinheim, 2001; Vol. 2, pp 270-337. (5) (a) Verhoeven, J. W.; van Ramesdonk, H. J.; Groeneveld, M. M.; Benniston, A. C.; Harriman, A. ChemPhysChem 2005, 6, 2251. (b) Verhoeven, J. W. J. Photochem. Photobiol. C 2006, 7, 40. (6) Maggini, M.; Guldi, D. M. In Molecular and Supramolecular Photochemistry; Ramamurthy, V., Schanze, K. S., Eds.; Marcel Dekker Inc.: New York, 2001; Vol. 7, pp 149-196. (7) (a) Williams, R. M.; Zwier, J. M.; Verhoeven, J. W. J. Am. Chem. Soc. 1995, 117, 4093. (b) Williams, R. M.; Koeberg, M.; Lawson, J. M.; An, Y.-Z.; Rubin, Y.; Paddon-Row, M. N.; Verhoeven, J. W. J. Org. Chem. 1996, 61, 5055. (c) Thomas, K. G.; Biju, V.; George, M. V.; Guldi, D. M.; Kamat, P. V. J. Phys. Chem. A 1998, 102, 5341. (d) Thomas, K. G.; Biju, V.; Guldi, D. M.; Kamat, P. V.; George, M. V. J. Phys. Chem. A 1999, 103, 10755. (e) Komamine, S.; Fujitsuka, M.; Ito, O.; Moriwaki, K.; Miyata, T.; Ohno, T. J. Phys. Chem A. 2000, 104, 11497. (8) (a) Wang, Y. Nature 1992, 356, 585. (b) Wang, Y.; Suna, A. J. Phys. Chem. B 1997, 101, 5627. (9) (a) Watanabe, A.; Ito, O. J. Chem. Soc., Chem. Commun. 1994, 1285. (b) Sauve´, G. Dimitrijevic´, N. M.; Kamat, P. V. J. Phys. Chem. 1995, 99, 1199. (c) Itaya, A.; Suzuki, I.; Tsuboi, Y.; Miyasaka, H. J. Phys. Chem. B 1997, 101, 5118. (d) Yahata, Y.; Sasaki, Y.; Fujitsuka, M.; Ito, O. J. Photosci. 1999, 6, 117. (e) Fujitsuka, M.; Yahata, Y.; Watanabe, A.; Ito, O. Polymer 2000, 41, 2807. (f) T. Midorikawa, T.; Araki, Y.; Fujitsuka, M.; Ito, O. J. Nanosci. Nanotechnol. 2007, 7, 1419.
J. Phys. Chem. C, Vol. 112, No. 4, 2008 1249 (10) Zeng, H.-P.; Wang, T.; Sandanayaka, A. S. D.; Araki, Y.; Ito, O. J. Phys. Chem. A 2005, 109, 4713. (11) Nakamura, Y.; Suzuki, M.; Imai, Y.; Nishimura, J. Org. Lett. 2004, 6, 2797. (12) Nakamura, Y.; Konno, T.; Watanabe, S.; Suzuki, M.; Yoshihara, T.; Tobita, S.; Nishimura, J. Chem. Lett. 2007, 36, 264. (13) (a) Sandanayaka, A. S. D.; Ikeshita, K.; Rajkumar, G. A.; Furusho, Y.; Araki, Y.; Takata, T.; Ito, O. J. Phys. Chem. A. 2005, 109, 8088. (b) El-Khouly, M. E.; Hasegawa, J.; Momotake, A.; Sasaki, M.; Araki, Y.; Ito, O.; Arai, T. J. Porphyrins Phthalocyanines 2006, 10, 1380. (14) (a) Kimoto, A.; Cho, J.-S.; Higuchi, M.; Yamamoto, K. Macromolecules 2004, 37, 5531. (b) McClenaghan, N. D.; Passalacqua, R.; Loiseau, F.; Campagna, S.; Verheyde, B.; Hameurlaine, A.; Dehaen, W. J. Am. Chem. Soc. 2003, 125, 5356. (15) Loiseau, F.; Campagna, S.; Hameurlaine, A.; Dehaen, W. J. Am. Chem. Soc. 2005, 127, 11352. (16) (a) Principles of Fluorescence Spectroscopy, 2nd edition; Lakowicz, J. R., Ed.; Kluwer Academic: New York, 1999. (b) D’ Souza, F.; Deviprasad, G. R.; El-Khouly, M. E.; Fujitsuka, M.; Ito, O. J. Am. Chem. Soc. 2001, 123, 5277. (17) Rehm, D.; Weller, A. Isr. J. Chem. 1970, 8, 259. (18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision B-04; Gaussian, Inc.: Pittsburgh, PA, 2003. (19) (a) Ito, O.; Sasaki, Y.; Yoshikawa, Y.; Watanabe. A. J. Phys. Chem. 1995, 99, 9838. (b) Ito, O. Res. Chem. Intermed. 1997, 23, 389. (20) (a) Arbogast, J. W.; Foote, C. S.; Kao, M. J. Am. Chem. Soc. 1992, 114, 2277. (b) Steren, C. A.; von Willigen, H.; Biczo´k, L.; Gupta, N.; Linschitz, H. J. Phys. Chem. 1996, 100, 8920. (21) Electronic Absorption Spectra of Radical Ions; Shida, T., Ed.; Elsevier Science Publishing Company: Amsterdam, The Netherlands, 1988; p 212. (22) (a) Marcus, R. A.; Sutin, N. Biochim. Biophys. Acta 1985, 811, 265. (b) Marcus, R. A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1111. (23) (a) Sandanayaka, A. S. D.; Matsukawa, K.; Ishi-i, T.; Mataka, S.; Araki, Y.; Ito, O. J. Phys. Chem. B 2004, 108, 19995. (b) Sandanayaka, A. S. D.; Sasabe, H.; Araki, Y.; Furusho, Y.; Ito, O.; Takata, T. J. Phys. Chem. A 2004, 108, 5145. (24) (a) Fujitsuka, M.; Ito, O.; Yamashiro, T.; Aso, Y.; Otsubo, T. J. Phys. Chem. A 2000, 104, 4876. (b) Yamazaki, M.; Araki, Y.; Fujitsuka, M.; Ito, O. J. Phys. Chem. A 2001, 105, 8615. (c) Nakamura, T.; Kanato, H.; Araki, Y.; Ito, O.; Takimiya, K.; Otsubo, T.; Aso, Y. J. Phys. Chem. A 2006, 110, 3471.